This invention relates to a single needle blood pump system, and particularly to such a system wherein blood flow and pressure are easily regulated.
In the use of an "artificial kidney", dialysis of the patient's blood requires some means of withdrawing the blood from the patient's body and returning the same after treatment. With cannulae, providing permanent tubular connection to the patient, connection of the patient to the dialyzer apparatus is facilitated. However, a patient may not tolerate this arrangement because of infection or the like. Alternatively, plural hypodermic needles may be inserted in a patient's vein after insertion of a fistula between a vein and artery, with one needle being utilized for withdrawal of blood while a second needle is employed to return blood to the vein. A more desirable system would avoid the requirement for repeated insertion of both needles.
A prior art single needle system withdraws and returns blood via the same hypodermic needle and includes a pair of clamp valves employed in two connections to the hypodermic needle so that blood can be alternately withdrawn and returned therethrough. In this system the valves are solenoid operated in response to pressure detected at a dialyzer output. However, pumping in such a system tends to produce a vacuum at the pump inlet, flattening the plastic tubing and causing cessation of system operation.
According to copending application Ser. No. 348,509 entitled "Single Needle Alternating Flow Blood Pump System" filed Apr. 6, 1973, by Charles B. Willock, incorporated herein by reference, a single needle system comprises a blood flow loop including a blood pump and valve means operated by the blood pump for returning blood to the patient when the pump is periodically turned off. This system has the advantage of simplicity, reliability and absence of dependence upon detected pressure. Moreover, the periodically operating pump does not cause flattening of the plastic tubing in the blood flow loop.